As we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns -- the ones we don't know we don't know. — Donald Rumsfeld, February 12 , 2002.

TORONTO - A giant ice shelf has snapped free from an island south of the North Pole, scientists said Thursday, citing climate change as a "major" reason for the event.

The Ayles Ice Shelf all 41 square miles of it broke clear 16 months ago from the coast of Ellesmere Island, about 500 miles south of the North Pole in the Canadian Arctic.

Warwick Vincent of Laval University, who studies Arctic conditions, traveled to the newly formed ice island and couldn't believe what he saw.

"This is a dramatic and disturbing event. It shows that we are losing remarkable features of the Canadian North that have been in place for many thousands of years," Vincent said. "We are crossing climate thresholds, and these may signal the onset of accelerated change ahead."

The ice shelf was one of six major shelves remaining in Canada's Arctic. They are packed with ancient ice that is more than 3,000 years old. They float on the sea but are connected to land.

Some scientists say it is the largest event of its kind in Canada in 30 years and that climate change was a major element.

"It is consistent with climate change," Vincent said, adding that the remaining ice shelves are 90 percent smaller than when they were first discovered in 1906. "We aren't able to connect all of the dots ... but unusually warm temperatures definitely played a major role."

. . .

[Luke Copland, head of the new global ice lab at the University of Ottawa]said the speed with which climate change has effected the ice shelves has surprised scientists.

"Even 10 years ago scientists assumed that when global warming changes occur that it would happen gradually so that perhaps we expected these ice shelves just to melt away quite slowly," he said.

Derek Mueller, a polar researcher with Vincent's team, said the ice shelves get weaker and weaker as temperatures rise. He visited Ellesmere Island in 2002 and noticed that another ice shelf had cracked in half.

"We're losing our ice shelves and this a feature of the landscape that is in danger of disappearing altogether from Canada," Mueller said.

Earlier this week, President Bush's administration moved to recognize polar bears as endangered due to the extreme reduction in available ice floes where they fish.